Mercury 150HP Lanyard Swith Blowing 15AMP Helm Fuse (#2B750768)

[Action1820]

Good Afternoon Everyone-

Trying to run down an electrical issue on my 2020 Mercury 150 4-Stroke. (Serial #2B750768 / Model #1150F23ED) Whenever the key switch is on, and the lanyard is pulled, the 15 amp helm fuse blows immediately. My kill switch is part of the throttle and not separate on the console. My understanding of the kill switch is that when it is activated, similar to turning the key to off, the circuit is grounded. Blowing a fuse instantly would indicate a short circuit to me - is it grounding thru the PCM, or directly to the boat grounds? If PCM, that would lead me to start running down a short circuit somewhere in the helm / throttle, as turning the key off isn't blowing the fuse. If its grounding to the boat grounds, where would I start trying to run this down? Are there any specific resistances I should be / not be seeing through that switch?

Thanks-

Josh

[EuropeanAM]

Check the lanyard switch itself to see if all THREE (3) wires are connected. If so, remove the PURPLE wire from the kill switch and see if that doesn't resolve the problem for you.

[Action1820]

Good Evening Don-

Apologies for the long delay in response here - getting to the kill switch necessitated removing the control. I was able to get it removed from the boat today. Looking at the kill switch, it only has two wires. There is a black with yellow stripe and solid black going to the switch. The switch was wrapped in electrical tape, which looked odd to me. I pulled the wires out and was able to get to the splices. The black wire ties back to a yellow wire (yellow on this boat is ground), and the black with yellow ties into a butt connector with two more black with yellow stripes.

I left the throttle apart to perform additional diagnostics. Is there somewhere I should start looking at OHMing out or testing? binncle 1.jpgbinnacle 2.jpg

The control is

[EuropeanAM]

What is the label on that "Yellow" wire?

The ONLY wire colors you should have at the lanyard would be Black, Black w/Yellow Stripe (and in some cases, purple).

Your blowing fuse when lanyard is OFF and key is turned on tends to indicate that there is a short circuit between the key switch power circuit and the lanyard GROUND circuit.

That yellow wire is not a normal component of the Mercury Rigging.

[Action1820]

The yellow wire label is just a number. On this boat, all of the grounds are with yellow wires. I ohmed it back to both the helm ground block, the rear ground block, and the negative terminal on the battery to confirm its a ground. Continuing to ohm out, with the key off, im showing an open line / infinite resistance from that kill switch ground lead to the purple and other lines on the keyswitch, except the yellow ground one. When I turn the key on (but leave battery off), im getting low but increasing resistance on my meter on both the purple and the red with purple stripe wires to the ground. After a few seconds the beeping goes away on my meter, but its not showing an open line - there is some sort of contact there.

I have noticed recently as well that when I turn the key switch to off, the motor take a second or two to shut off - its not instant like I remember.

Is my next step to run a new ground wire from the kill switch and bypass the current one? Or is it possible the issue is in the keyswitch itself? I would think the same fuse would blow if the short was in the keyswitch, as the off and kill switch share that black with yellow stripe.

Thanks Don-

Josh

[EuropeanAM]

Likely a bad key switch. I would disconnect it completely, and test for ANY continuity between the "M" (BLACK, in this case Yellow) and the RED (B) or Purple (I) circuits.

There should be NO continuity in ANY key position.